The invention relates to scintillation cameras, and more particularly relates to scintillation cameras for transaxial ECT (Emission Computed Tomography) imaging. In its most immediate sense the invention relates to tomographic imaging of relatively small body organs such as the heart.
When constructing tomographic images of a small body organ (such as the heart) using transaxial ECT, the scintillation camera head with a collimator attached is rotated around the patient. To prevent the tomographic image from being marred by artifacts, it is necessary to image not merely the heart alone, but the entire slice of the body in which the heart is located. When the collimator used is a fan-beam collimator, the collimator conventionally has a comparatively long focal length, such as 130 centimeters, so that the views of the body are not truncated. This in turn insures that there is complete sampling around the heart and prevents artifacts caused by truncation.
This focal length is appropriate for imaging the periphery of the body, but it inappropriately establishes the sensitivity of the collimator. This is because for fixed resolution and radius of rotation, sensitivity decreases as focal length increases. By choosing a single focal length which is just long enough to include the periphery of the body, the sensitivity gain of the collimator is limited by the periphery of the body (which is not generally of interest) rather than by a central body organ of interest (i.e. the heart).
It is therefore one object of the invention to provide a transaxial ECT scintillation camera system which has improved sensitivity in its center without causing truncation errors and corresponding artifacts.
It is another object to provide such a system which will improve images of comparatively small body organs, such as the heart.
It is another object to, in general, improve on known systems of this type.